MARCH 1998
IC026A-R2
IC026AE-R2
RS-232↔IEEE 488
Interface Converter
POWER
ERROR
SRQ
LISTEN
ALK
T
CUSTOMER Order toll-free in the U.S. 24 hours, 7 A.M. Monday to midnight Friday: 877-877-BBOX
FREE technical support, 24 hours a day, 7 days a week: Call 724-746-5500 or fax 724-746-0746
Mail order: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
SUPPORT
INFORMATION
Web site: www.blackbox.com
•
E-mail: [email protected]
Download from Www.Somanuals.com. All Manuals Search And Download.
WARNING!
Noted conditions pertain to potential safety hazards. When you see a
WARNING!, CAUTION!, or IMPORTANT! note, carefully read the
information and be alert to the possibility of personal injury.
Failure to follow these directives voids emission and immunity compliance.
TRADEMARKS USED IN THIS MANUAL
®
®
®
AT , IBM , and PS/2 are registered trademarks, and PC/XT is a trademark,
of IBM Corporation.
®
Macintosh is a registered trademark of Apple Computer, Inc.
®
®
®
Hewlett-Packard , HP , and HP-GL are registered trademarks of Hewlett-Packard.
®
AutoCAD is a registered trademark of AUTODESK, Inc.
®
MacPlot is a registered trademark of Microspot Ltd.
All applied-for and registered trademarks are the property of their respective owners.
3
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
FEDERAL COMMUNICATIONS COMMISSION
AND
INDUSTRY CANADA
RADIO FREQUENCY INTERFERENCE STATEMENTS
This equipment generates, uses, and can radiate radio frequency energy
and if not installed and used properly, that is, in strict accordance with the
manufacturer’s instructions, may cause interference to radio communication.
It has been tested and found to comply with the limits for a Class A computing
device in accordance with the specifications in Subpart J of Part 15 of FCC
rules, which are designed to provide reasonable protection against such
interference when the equipment is operated in a commercial environment.
Operation of this equipment in a residential area is likely to cause interference,
in which case the user at his own expense will be required to take whatever
measures may be necessary to correct the interference.
Changes or modifications not expressly approved by the party responsible
for compliance could void the user’s authority to operate the equipment.
This digital apparatus does not exceed the Class A limits for radio noise emission from
digital apparatus set out in the Radio Interference Regulation of Industry Canada.
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les limites
applicables aux appareils numériques de classe A prescrites dans le Règlement sur le
brouillage radioélectrique publié par Industrie Canada.
4
Download from Www.Somanuals.com. All Manuals Search And Download.
NOM STATEMENT
NORMAS OFICIALES MEXICANAS (NOM)
ELECTRICAL SAFETY STATEMENT
INSTRUCCIONES DE SEGURIDAD
1. Todas las instrucciones de seguridad y operación deberán ser leídas
antes de que el aparato eléctrico sea operado.
2. Las instrucciones de seguridad y operación deberán ser guardadas para
referencia futura.
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones
de operación deben ser respetadas.
4. Todas las instrucciones de operación y uso deben ser seguidas.
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo,
cerca de la tina de baño, lavabo, sótano mojado o cerca de una alberca,
etc..
6. El aparato eléctrico debe ser usado únicamente con carritos o pedestales
que sean recomendados por el fabricante.
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como
sea recomendado por el fabricante.
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico más
allá a lo descrito en las instrucciones de operación. Todo otro servicio
deberá ser referido a personal de servicio calificado.
9. El aparato eléctrico debe ser situado de tal manera que su posición no
interfiera su uso. La colocación del aparato eléctrico sobre una cama,
sofá, alfombra o superficie similar puede bloquea la ventilación, no se
debe colocar en libreros o gabinetes que impidan el flujo de aire por
los orificios de ventilación.
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de
calor como radiadores, registros de calor, estufas u otros aparatos
(incluyendo amplificadores) que producen calor.
5
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo
del tipo descrito en el instructivo de operación, o como se indique en
el aparato.
12. Precaución debe ser tomada de tal manera que la tierra fisica y la
polarización del equipo no sea eliminada.
13. Los cables de la fuente de poder deben ser guiados de tal manera que no
sean pisados ni pellizcados por objetos colocados sobre o contra ellos,
poniendo particular atención a los contactos y receptáculos donde salen
del aparato.
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las
recomendaciones del fabricante.
15. En caso de existir, una antena externa deberá ser localizada lejos
de las lineas de energia.
16. El cable de corriente deberá ser desconectado del cuando el equipo
no sea usado por un largo periodo de tiempo.
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean
derramados sobre la cubierta u orificios de ventilación.
18. Servicio por personal calificado deberá ser provisto cuando:
A: El cable de poder o el contacto ha sido dañado; u
B: Objectos han caído o líquido ha sido derramado dentro del
aparato; o
C: El aparato ha sido expuesto a la lluvia; o
D: El aparato parece no operar normalmente o muestra un cambio
en su desempeño; o
E: El aparato ha sido tirado o su cubierta ha sido dañada.
6
Download from Www.Somanuals.com. All Manuals Search And Download.
CONTENTS
Contents
Chapter
Page
1. Specifications..................................................................................................10
2. Introduction ...................................................................................................12
2.1 Description ............................................................................................12
2.2 Abbreviations.........................................................................................13
3. Getting Started ...............................................................................................14
3.1 Inspection ..............................................................................................14
3.2 Configuration ........................................................................................14
3.3 Serial Port Settings ................................................................................16
3.3.1 Serial Baud Rate ........................................................................16
3.3.2 Serial Word Length (Data Bits)................................................18
3.3.3 Serial Stop Bits...........................................................................18
3.3.4 Serial Parity ................................................................................19
3.3.5 Serial Echo .................................................................................19
3.3.6 Serial Handshake.......................................................................20
3.4 Selecting Terminator Substitution.......................................................21
3.4.1 Serial Terminator ......................................................................21
3.4.2 IEEE Bus Terminator ................................................................22
3.5 Selecting the Mode ...............................................................................22
3.6 Selecting the IEEE Address ..................................................................23
3.7 Feature Selections .................................................................................24
3.7.1 Controller Features ...................................................................24
3.7.2 Peripheral Features ...................................................................25
3.8 Serial Interface ......................................................................................25
3.8.1 RS-232/RS-422 Signal Level Selection .....................................26
3.8.2 Serial Signal Descriptions..........................................................26
3.8.3 Serial-Cable Wiring Diagrams...................................................29
3.9 General Operation................................................................................30
4. Controller Operation.....................................................................................32
4.1 Controller-Mode (Serial to IEEE) Operation .....................................32
4.2 Serial and IEEE Terminator Substitution............................................33
4.3 IEEE Address Selection.........................................................................34
7
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Chapter
Page
4.4 Talk-Back Features ................................................................................34
4.4.1 Talk-Back on Terminator..........................................................34
4.4.2 Talk-Back on Timeout...............................................................36
4.5 Plotter Applications...............................................................................38
4.6 Printer Applications ..............................................................................44
5. Peripheral Operation.....................................................................................45
5.1 Peripheral-Mode Operation .................................................................45
5.2 Serial and IEEE Input Buffers ..............................................................45
5.3 IEEE Data Transfers..............................................................................46
5.3.1 Blind Bus Data Transfers...........................................................46
5.3.2 Controlled Bus Data Transfers .................................................47
5.4 Serial-Poll Status-Byte Register .............................................................48
5.5 Use of Serial and Bus Terminators ......................................................50
5.6 IEEE 488 Bus Implementation.............................................................50
5.6.1 My Talk Address (MTA)............................................................51
5.6.2 My Listen Address (MLA).........................................................51
5.6.3 Device Clear (DCL and SDC)...................................................51
5.6.4 Interface Clear (IFC).................................................................51
5.6.5 Serial Poll Enable (SPE)............................................................51
5.6.6 Serial Poll Disable (SPD) ..........................................................51
5.6.7 Unlisten (UNL) .........................................................................51
5.6.8 Untalk (UNT)............................................................................51
5.7 IEEE Address Selection.........................................................................52
6. IEEE 488 Primer.............................................................................................53
6.1 History....................................................................................................53
6.2 General Structure..................................................................................53
6.3 Send It To My Address..........................................................................55
6.4 Bus Management Lines.........................................................................56
6.4.1 Attention (ATN)........................................................................56
6.4.2 Interface Clear (IFC).................................................................56
6.4.3 Remote Enable (REN) ..............................................................56
6.4.4 End Or Identify (EOI) ..............................................................56
6.4.5 Service Request (SRQ)..............................................................56
8
Download from Www.Somanuals.com. All Manuals Search And Download.
CONTENTS
Chapter
Page
6.5 Handshake Lines...................................................................................57
6.5.1 Data Valid (DAV).......................................................................57
6.5.2 Not Ready For Data (NRFD) ....................................................57
6.5.3 Not Data Accepted (NDAC) .....................................................57
6.6 Data Lines..............................................................................................58
6.7 Multiline Commands ............................................................................58
6.7.1 Go To Local (GTL) ...................................................................58
6.7.2 Listen Address Group (LAG)....................................................58
6.7.3 Unlisten (UNL) .........................................................................59
6.7.4 Talk Address Group (TAG) ......................................................59
6.7.5 Untalk (UNT)............................................................................59
6.7.6 Local Lockout (LLO)................................................................59
6.7.7 Device Clear (DCL)...................................................................59
6.7.8 Selected Device Clear (SDC) ....................................................59
6.7.9 Serial Poll Disable (SPD) ..........................................................59
6.7.10 Serial Poll Enable (SPE)..........................................................59
6.7.11 Group Execute Trigger (GET)...............................................59
6.7.12 Take Control (TCT)................................................................60
6.7.13 Secondary Command Group (SCG) ......................................60
6.7.14 Parallel Poll Configure (PPC).................................................60
6.7.15 Parallel Poll Unconfigure (PPU)............................................60
6.8 More on Service Requests.....................................................................60
6.8.1 Serial Poll ...................................................................................61
6.8.2 Parallel Poll................................................................................61
7. Theory of Operation and Board Layout.......................................................62
7.1 Theory of Operation.............................................................................62
7.2 Board Layout .........................................................................................63
Appendix A: Sample Dumb-Terminal Program...............................................65
Appendix B: Character Codes and IEEE Multiline Messages .........................66
Index...................................................................................................................68
9
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
1. Specifications
IEEE-488 Interface
Implementation —
C1, C2, C3, C4, and C28 controller subsets.
Serial to IEEE: SH1, AH1, T6, TE0, L4, LE0,
SR1, RL0, PP0, DC1, DT0, E1.
Terminators —
Selectable CR, LF, LF-CR, and CR-LF
with EOI
Connector —
Standard IEEE 488 connector with metric studs
Serial Interface
EIA RS-232C —
EIA RS-422A —
Character Set —
Output Voltage —
AB, BA, BB, CA, CB
Balanced voltage on TxD and RxD
Asynchronous bit serial
5 volts min. (RS-232C);
5 volts typical (RS-422A)
Input Voltage —
Baud Rate —
3 volts min.; q15v max.
Selectable 110, 300, 600, 1200, 1800, 2400,
3600, 4800, 7200, 9600, 19,200, and 57,600
Data Format —
Selectable 7 or 8 data bits; 1 or 2 stop bits;
odd, even, mark, space, and no parity on
transmit
Duplex —
Full with Echo/No Echo
Serial Control —
Terminators —
Connector —
Selectable CTS/RTS or XON/XOFF
Selectable CR, LF, LF-CR, and CR-LF
25-pin sub-D male, DCE configured
10
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 1: Specifications
General
Data Buffer —
32,000 characters dynamically allocated
Indicators —
LEDs for IEEE Talk and Listen, Serial Send
and Receive, and Power
Power —
105-125V or 210-250V; 50-60 Hz, 10 VA max.
2.7"H x 5.5"W x 7.4"D (6.9 x 14 x 18.8 cm)
3.6 lb. (1.6 kg)
Size —
Weight —
Environment —
0 to 50°C; 0 to 70% R.H. to 35°C.
Linearly derate 3% R.H./degrees Centigrade
from 35 to 50°C
Controls —
Power Switch (external), IEEE and Serial
parameter switches (internal). Jumper
selection of RS-232 or RS-422 operation
(internal)
Certification —
FCC, CE
WARNING!
Do not use this interface outdoors. The interface is intended for indoor
use only. Using this equipment outdoors could result in equipment
failure, bodily injury, or death.
CAUTION
Do not connect AC line power directly to the RS-232↔IEEE 488 Interface
Converter. Direct AC connection will damage equipment.
11
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
2. Introduction
2.1 Description
The RS-232↔488 Interface Converter provides transparent communication
from a serial computer to an IEEE 488 printer, plotter, or other device. It also
can be used to control a serial device, such as a printer or terminal, from an
IEEE 488 host computer.
As a serial-to-IEEE-488 converter, the interface converter receives data from
a serial host then automatically performs the bus sequences necessary to send
this data to the IEEE 488 device. If desired, data can be requested from the
IEEE 488 device and returned to the host.
As an IEEE 488 to serial converter the interface converter is a peripheral to
an IEEE 488 controller. Data received from the controller is sent to the serial
device, and the data received from the serial device is buffered for trans-
mission to the IEEE 488 controller. The interface converter can inform
the host, by the serial poll-status byte, that it has received data from the
serial device.
12
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 2: Introduction
2.2 Abbreviations
The IEEE 488 abbreviations listed below are used throughout this manual.
addr n
ATN
CA
IEEE bus address “n”
Attention line
Controller Active
Controller
CO
CR
Carriage Return
Data String
Device Clear
Group Execute Trigger
Go To Local
Listener Active
Listen Address Group
Line Feed
data
DCL
GET
GTL
LA
LAG
LF
LLO
MLA
MTA
PE
PPC
PPU
SC
SDC
SPD
SPE
SRQ
TA
TAD
TCT
term
UNL
UNT
*
Local Lock Out
My Listen Address
My Talk Address
Peripheral
Parallel Poll Configure
Parallel Poll Unconfigure
System Controller
Selected Device Clear
Serial Poll Disable
Serial Poll Enable
Service Request
Talker Active
Talker Address
Take Control
Terminator
Unlisten
Untalk
Unasserted
13
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3. Getting Started
3.1 Inspection
The interface converter was carefully inspected, both mechanically and
electrically, prior to shipment. When you receive it, carefully unpack all items
from the shipping carton and check for any obvious signs of damage that may
have occurred during shipment. Immediately report any damage found to the
shipping agent. Remember to retain all shipping materials in the event that
shipment back to the factory becomes necessary.
Every interface converter is shipped with the following:
• RS-232↔IEEE 488 Interface Converter
• This instruction manual
• Power supply
3.2 Configuration
Three DIP switches internal to the interface converter set the configuration
of the interface.
NOTE
Selectable functions are read only at power-on and should only be set
prior to applying power to the interface. The following figures illustrate
the factory-default conditions, which are:
Serial Port:
IEEE:
9600 Baud
Mode = IEEE 488 Controller
Address = 10
Bus Terminator = LF; EOI Disabled
Talk-Back on Terminator Enabled
Talk-Back on Timeout Enabled
8 Data Bits
2 Stop Bits
No Parity
Serial Terminator = LF
Echo Disabled
RTS/CTS Handshake
14
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
10
LF
Disabled
IEEE Addr
IEEE Term
EOI
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
C
Mode
Talk-Back on Timeout
Serial Term
Enabled
LF
No Echo
No Parity
Echo
Parity
DOT
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
9600
RTS/CTS
8 Data Bits
Enabled
2 Stop Bits
Baud Rate
Handshake
Word Length
Talk-Back on Term
Stop Bits
Figure 3-1. Factory-Default Settings.
15
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Note that the interface converter comes configured as an IEEE controller. In
this mode, the interface converter is designed to allow an RS-232 computer to
communicate with an IEEE peripheral such as a plotter. This controller mode
is described in detail in Chapter 4.
The interface converter may also be configured as an IEEE peripheral. As an
IEEE peripheral, it allows an IEEE controller to communicate with an RS-232
device. The peripheral mode of operation is described in detail in Chapter 5.
To modify any of these defaults, follow this simple procedure:
1. Disconnect the power supply from the AC line and from the interface. Also
disconnect any IEEE or serial cables.
WARNING
Never open the interface converter’s case while it is connected to the AC
line. Failure to observe this warning may result in equipment failure,
personal injury, or death.
2. Place the interface converter upside down on a flat surface. Remove the
four screws located near the rubber feet.
3. Return the interface converter to the upright position and carefully remove
the top cover.
4. Change whichever DIP-switch settings you need to change.
5. When you have made all your changes, reverse this procedure to
reassemble the interface converter.
3.3 Serial Port Settings
The first parameters to configure are those that correspond to the RS-232
port. These include baud rate, word length, number of stop bits, parity
selection and type of RS-232 handshake. Each of these are described in
the following sections.
3.3.1 SERIAL BAUD RATE
The “baud rate” is the number of serial data bits per second transferred into
and out of the RS-232 interface. SW1-1 through SW1-4 determine the serial
baud rate. The factory-default baud rate is 9600 baud. Baud rates may be
selected from 110 to 57,600 baud. Refer to the following diagram for specific
baud rates.
16
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
DOT
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
4
5
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
4
5
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
Switch
Side
View
110
110
1800
2400
OPEN
OPEN
4
5
4
5
OPEN
OPEN
4
5
4
5
110
3600
OPEN
OPEN
4
5
4
5
135
15 0
300
600
1200
4800
OPEN
OPEN
4
5
4
5
7200
OPEN
OPEN
4
5
4
5
9600
OPEN
OPEN
4
5
4
5
19,200
57,600
OPEN
OPEN
4
5
4
5
OPEN
OPEN
Figure 3-2. Switch SW1: Selecting the Serial Baud Rate.
17
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3.3.2 SERIAL WORD LENGTH (DATA BITS)
SW1-6 determines the number of data bits, often referred to as word length,
for each serial character transmitted or received. The factory default is 8 data
bits.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
8 Data Bits
7 Data Bits
Figure 3-3. Switch SW1: Selecting the Serial Word Length (Data Bits).
3.3.3 SERIAL STOP BITS
Switch SW1-8 determines the number of stop bits contained in each serial
character transmitted and received. The factory default is 2 stop bits.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
1 Stop Bit
2 Stop Bits
Figure 3-4. Switch SW1: Selecting the Serial Stop Bits.
18
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
3.3.4 SERIAL PARITY
Serial Parity is selected with S2-6 through S2-8. The interface converter
generates the selected parity during serial transmissions but it does not
check parity on data that is received. The factory default is parity disabled.
DOT
1
1
2
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Odd Parity
Mark Parity
3
4
5
6
7
8
1
2
3
4
5
6
7
8
OPEN
OPEN
Even Parity
Space Parity
1
2
3
4
5
6
7
8
OPEN
Parity Disabled
Figure 3-5. Switch SW2: Selecting the Serial Parity.
3.3.5 SERIAL ECHO
Serial data sent to the interface converter will be echoed back to the serial
host if SW2-5 is set to the open position. The factory default is Echo Disabled.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Echo Disabled
Echo Enabled
Figure 3-6. Switch SW2: Enabling or Disabling Echo.
19
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3.3.6 SERIAL HANDSHAKE
Switch SW1-5 is used to select hardware [RTS/CTS] or software [Xon/Xoff]
serial handshake control.
With X-ON/X-OFF, the interface converter issues an X-OFF character [ASCII
value of $13] when its buffer memory is near full. When the X-OFF character
is sent, there are still more than 1000 character locations remaining to protect
against buffer overrun. When it is able to accept more information, the inter-
face converter issues an Xon character [ASCII value of $11]. The interface
converter also accepts X-ON/X-OFF on transmit from the serial host it is
communicating with. RTS/CTS serial control becomes inactive when X-
ON/X-OFF is enabled. The RTS output is, however, set to an active high
state. The CTS input is not used for this handshake and may be left
floating (unconnected).
With RTS/CTS, the interface converter un-asserts RTS (sets RTS low) when
its buffer memory is near full. When RTS is un-asserted, there are still more
than 1000 character locations remaining to protect against buffer overrun.
When it is able to accept more information, the interface converter asserts
RTS (sets RTS high). The interface converter will not transmit data to the
serial host if it detects the CTS input un-asserted (low) when configured
for this hardware handshake.
The factory-default serial control is hardware, RTS/CTS.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
RTS/CTS
X-ON/X-OFF
Figure 3-7. Switch SW1: Selecting the Serial Handshake.
20
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
3.4 Selecting Terminator Substitution
The interface converter can be configured to provide RS-232-to-IEEE-488 and
IEEE-488-to-RS-232 terminator substitution. This is useful when interfacing an
RS-232 device which only issues carriage return [CR] as an output terminator
to an IEEE controller which expects a carriage return followed by a line feed
[CR-LF].
In a case like that, the serial terminator should be selected for CR Only while
the IEEE terminator is set to CR-LF. When a serial CR character is received,
it is discarded, and an IEEE CR-LF is substituted for it. In the IEEE-to-RS-232
direction, the IEEE CR is unconditionally discarded. Upon receipt of the
IEEE LF, a serial CR is substituted.
The interface converter can be made totally data transparent by setting both
the serial and IEEE terminators to be CR Only or LF Only.
3.4.1 SERIAL TERMINATOR
SW2-3 and SW2-4 select the serial terminators for the serial input and output.
The factory default is LF Only.
DOT
1
1
2
2
3
4
5
6
7
7
8
8
1
1
2
2
3
3
4
5
6
6
7
7
8
8
Switch
Side
View
OPEN
OPEN
CR Only
LF-CR
3
4
5
6
4
5
OPEN
OPEN
LF Only
CR-LF
Figure 3-8. Switch SW2: Selecting the Serial Terminator.
21
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3.4.2 IEEE BUS TERMINATOR
SW3-6 through SW3-8 set the IEEE bus terminators used for data sent or
received by the interface converter. EOI, a line used to signal the end of
a multiple character bus transfer, may also be enabled. If enabled, EOI
is asserted when the last selected bus terminator is sent. Factory default
is LF Only with EOI disabled.
DOT
1
1
1
2
2
2
3
4
5
6
7
7
7
8
8
8
1
1
1
2
2
2
3
3
3
4
5
6
7
7
7
8
8
8
Switch
Side
View
OPEN
OPEN
CR Only
LF-CR
3
4
5
6
4
5
6
OPEN
OPEN
LF Only
CR-LF
3
4
5
6
4
5
6
OPEN
OPEN
EOI Disabled
EOI Enabled
Figure 3-9. Switch SW3: Selecting the IEEE Bus Terminator.
3.5 Selecting the Mode
SW2-1 sets the major operating mode of the interface converter. The IEEE
Controller (RS-232-to-IEEE converter) mode allows a serial host device to
send data to a single IEEE bus peripheral. Applications include interfacing
a listen-only or addressable IEEE printer/plotter to a serial printer port.
Refer to Chapter 4 for more detailed information on the controller mode
of operation.
The Peripheral mode is used when interfacing a serial device to an IEEE
controller. Data which is sent by the IEEE controller to the interface
converter is transmitted out its serial port. Data received from the serial
device is buffered by the interface converter until read by the IEEE controller.
Refer to Chapter 5 for more detailed information on the peripheral mode
of operation.
The factory default is the IEEE Controller mode, an RS-232-to-IEEE
converter.
22
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Controller Mode
Peripheral Mode
Figure 3-10. Switch SW2: Selecting the Mode.
3.6 Selecting the IEEE Address
SW3-1 through SW3-5 select the IEEE bus address of the interface converter
when in the IEEE Peripheral mode. These same switches are used in the IEEE
Controller mode to select the address of the device that will be controlled.
[Refer to Chapters 5 and 4 respectively for additional information]. The
address is selected by simple binary weighting, with SW3-1 being the least
significant bit and SW3-5 the most significant. The factory default is address 10.
Listen Only is a special type of Peripheral operation. In the Listen Only mode
the interface converter accepts all data transmitted on the bus, ignoring any
bus addressing, and transfers it out its serial port. The interface converter is
set to Listen Only mode by setting its address to 31. If the IEEE address is set
to 31 in the peripheral mode, it is adjusted to 30.
DOT
1
2
3
4
5
6
7
8
0
1
Switch
Side
View
OPEN
0 x 16 -0
1 x 8
0 x 4
1 x 2
-8
-0
-2
0 x 1 + -0
IEEE Address = 10
Figure 3-11. Switch SW3: Selecting the IEEE Address.
23
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3.7 Feature Selections
The functions of the remaining switches are dependent on the mode
selected. A brief description of each of these features follows. You should
refer to the listed sections for additional information.
3.7.1 CONTROLLER FEATURES
In the IEEE Controller (RS-232-to-IEEE 488 Converter) mode, SW1-7 is
used to determine whether the interface should, after sending the IEEE
bus terminators, address the attached bus device to talk. The factory default
is Talk-Back On Terminator enabled.
SW2-2 selects whether the interface converter should address the attached bus
device to talk when the interface converter has nothing more to send to that
device. The factory default is Talk-Back On Timeout enabled.
Refer to Chapter 4 for complete details on these features.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Talk-Back on
Terminator Disabled
Talk-Back on
Terminator Enabled
Figure 3-12. Switch SW1: Enabling or Disabling “Talk Back
on Terminator” in Controller Mode.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Talk-Back on
Timeout Disabled
Talk-Back on
Timeout Enabled
Figure 3-13. Switch SW2: Enabling or Disabling “Talk Back
on Timeout” in Controller Mode.
24
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
3.7.2 PERIPHERAL FEATURES
In the IEEE Peripheral (IEEE 488 to RS-232 converter) mode, SW1-7 enables
the interface to assert the SRQ IEEE bus interface line to indicate that it has
received the last switch selected serial terminator character from the serial
device.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
SRQ on Last
Terminator Disabled
SRQ on Last
Terminator Enabled
Figure 3-14. Switch SW1: Enabling or Disabling SRQ on Last Serial
Terminator in Peripheral Mode.
3.8 Serial Interface
The interface converter has the ability to output signal levels that are
compatible with either RS-232 or RS-422. An internal DIP shorting plug
determines which electrical specification is chosen. If the interface is to be
®
connected to an IBM PC or compatible, the RS-232 level should be selected.
®
If it will be connected to a Macintosh , the RS-422 level should be used. For
connection to other computers, refer to the manufacturer’s manual to
determine which levels are supported.
25
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
3.8.1 RS-232/RS-422 SIGNAL LEVEL SELECTION
The interface converter’s factory default signal levels are compatible with
RS-232. To select RS-422 levels, carefully remove the 8-position shorting plug
with a small flat blade screwdriver from J106. Install the DIP jumper into J205
making certain that all of the pins on the shorting plug are inserted correctly.
Shorting Plug
RS-422
RS-232
Figure 3-15. Selecting RS-232 or RS-422 Signal Levels.
3.8.2 SERIAL SIGNAL DESCRIPTIONS
The interface converter is equipped with a standard DB25 female connector
on its rear panel and requires a standard DB25 male mating connector. The
interface converter’s connector is configured as DCE type equipment for
RS-232 communications, which means the interface converter always trans-
mits data on Pin 3 and receives the data on Pin 2. The following lists and
describes the RS-232 and RS-422 signals provided on the interface converter.
26
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
13
25
1
14
Figure 3-16. Rear View of the Interface Converter’s Serial Connector.
-RxD
Receive Data—Input—Pin 2
This pin accepts serial data sent by the RS-232 or RS-422 host. The serial
data is expected with the word length, baud rate, stop bits, and parity
selected by the internal switches. The signal level is low true.
-TxD
Transmit Data—Output—Pin 3
This pin transmits serial data to the RS-232 or RS-422 host. The serial data
is sent with the word length, baud rate, stop bits, and parity selected by the
internal switches. The signal level is low true.
CTS
Clear To Send—Input—Pin 4
The CTS input is used as a hardware-handshake line to prevent the
interface converter from transmitting serial data when the RS-232 host
is not ready to accept it. When RTS/CTS handshake is selected on the
internal switches, the interface converter will not transmit data out -TxD
while this line is un-asserted (lowered). If the RS-232 host is not capable
of driving this line it can be connected to the Vtest output (Pin 6) of the
interface converter. If X-ON/X-OFF handshake is selected, the CTS line
is not tested to determine if it can transmit data.
RTS
Request To Send—Output—Pin 5
The RTS output is used as a hardware handshake line to prevent the
RS-232/RS-422 host from transmitting serial data if the interface converter
is not ready to accept it. When RTS/CTS handshake is selected on the
internal switches, the interface converter will drive the RTS output high
when there are more than 1,000 character locations available in its
internal buffer. If the number of available locations drops to less than
1,000, the interface converter will unassert (lower) this output. If
Xon/Xoff handshake is selected, the RTS line will be permanently
driven active (high).
27
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Vtest
Test Voltage—Output—Pin 6
This pin is connected to +5 volts through a 1K resistor. It is also common
to Vtest on Pin 9.
Gnd
Ground—Pin 7
This pin sets the ground reference point for the other RS-232 inputs and
outputs.
Vtest
Test Voltage—Output—Pin 9
This pin is connected to +5 volts through a 1K resistor. It is also common
to Vtest on Pin 6.
+RxD
Receive Data Plus—Input—Pin 14
This pin accepts serial data sent by the RS-422 host. The serial data is
expected with the word length, baud rate, stop bits, and parity selected by
the internal switches. The signal level is high true and only connected to
this pin when RS-422 operation is selected. It is 180 degrees out of phase
with -RxD.
+TxD
Transmit Data Plus—Output—Pin 16
This pin transmits serial data to the RS-422 host. The serial data is sent
with the word length, baud rate, stop bits, and parity selected by the
internal switches. The signal level is high true and only connected to
this pin when RS-422 operation is selected. It is 180 degrees out of phase
with -TxD.
28
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
3.8.3 SERIAL-CABLE WIRING DIAGRAMS
If a cable was not purchased with the interface, the following diagrams will be
helpful in making your own cable. Simple soldering skills and an attention to
detail will ensure successful construction.
Mini DINs Male
DB25 Male
RTS 1
CTS 2
-TxD 3
Gnd 4
-RxD 5
+TxD 6
+RxD 8
4 CTS
5 RTS
2 -RxD
7 Gnd
3 -TxD
14 +RxD
16 +TxD
Figure 3-17. Wiring Diagram:
Macintosh to Interface Converter (RS-422).
DB25 Female
DB25 Male
-TxD 2
-RxD 3
RTS 4
CTS 5
DSR 6
Gnd 7
2 -RxD
3 -TxD
4 CTS
5 RTS
3 V test
7 Gnd
Figure 3-18. Wiring Diagram: IBM PC or Compatible with
DB25 Serial Connector to Interface Converter (RS-232).
29
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
DB9 Female
DB25 Male
DCD 1
-RxD 2
-TxD 3
DTR 4
Gnd 5
DSR 6
RTS 7
3 -TxD
2 -RxD
7 Gnd
4 CTS
5 RTS
CTS 8
Figure 3-19. Wiring Diagram: IBM AT or Compatible with DB9 Serial
Connector to Interface Converter (RS-232).
NOTE
Standard AT 9-pin-to-25-pin adapter cables are not wired as shown
above and will not work with the interface converter.
3.9 General
Refer to the following sections for specific operational modes. This sub-
section gives a general test of functionality. After setting the power-on defaults
and reassembling the interface converter, plug the power-supply connector
into the rear jack on the interface.
CAUTION
Never plug the power supply into the interface while it is connected to
AC line power. If you do, you could damage the interface converter.
WARNING
The power supply provided with the interface converter is intended for
INDOOR USE ONLY. Using it outdoors could result in equipment failure,
personal injury, or death.
30
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 3: Getting Started
After plugging the power-supply connector into the interface, plug the power
supply into AC line power. Turn the rear-panel power switch ON (the “1”
position). All the front-panel indicators should light momentarily while the
interface converter performs an internal ROM and RAM self-check. At the
end of this self-check, all indicators except POWER should turn off.
If there is an error in the ROM checksum, all of the LEDs will remain on.
Flashing LEDs indicate a RAM failure. Should such an error occur, turn the
rear-panel switch to the OFF [0] position and retry the above procedure.
If the front-panel indicators do not flash and the POWER indicator does not
remain lit, there may not be any power supplied to the interface. In this event,
check the AC line and the rear-panel connection of the power supply. If the
problem is unresolved, call your supplier.
If proper operation is obtained, connect an interface cable to the DB25 port
on the rear of the interface converter. Connect the other end to the host’s
serial port. Except for connecting IEEE bus instruments, the interface
converter is installed and ready to use.
WARNING
The interface converter makes its earth-ground connection through the
serial interface cable. It should only be connected to the IEEE host.
Failure to do so may allow the interface converter to float to a bus-device
test voltage. This could result in damage to the interface, personal injury,
or death.
31
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
4. Controller Operation
4.1 Controller-Mode (Serial to IEEE) Operation
The IEEE Controller mode allows a serial RS-232 or RS-422 host device to
send data to a single IEEE bus peripheral or to multiple peripherals if they
occupy the same bus address. Applications include interfacing a listen-only
or addressable IEEE printer/plotter to a serial printer port.
Once the interface converter has initialized itself after power-on, it waits for
serial input data. When received, it addresses the selected IEEE device to
listen with the following bus sequence:
ATNUNL,MTA,LAG,*ATN
The data received from the serial host is placed into a circular serial input
buffer. Simultaneously, characters are removed from that buffer and sent
to the IEEE bus device. The serial terminator(s), if present, are not sent.
Instead, the IEEE terminators are substituted and sent in their place.
As long as the serial input buffer is not empty, the interface converter will
continue to send data from it to the IEEE bus device. If the serial input buffer
becomes emptied, the interface converter will command the IEEE bus device
to talk if one of the talk-back features is enabled. This allows the interface
converter to be used as a controller with devices, such as plotters or
instruments, that return status and other information to the host computer.
When the interface converter addresses the IEEE bus device to talk it uses the
following bus sequence:
ATNUNL,MLA,TAG,*ATN
The interface converter then accepts data from the IEEE device and returns
it to the host until the last selected IEEE terminator is detected. The IEEE bus
terminators are replaced by the serial terminators, and these are then sent to
the serial host.
If the IEEE device has been addressed to talk but does not respond or finish
transmission by the time additional characters are received in the circular
serial-input buffer, the talk sequence will be aborted to allow additional
serial information to be sent to the IEEE device.
32
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
4.2 Serial and IEEE Terminator Substitution
The interface converter can be configured to provide serial-to-IEEE-488 and
IEEE-488-to-serial terminator substitution. This is useful when interfacing a
serial host which only issues carriage return [CR] as an output terminator to
an IEEE peripheral which expects a carriage return followed by a line feed
[CR-LF].
In this case, the serial terminator should be selected for CR Only while the
IEEE terminator is set for CR-LF. When a serial CR character is received, it is
discarded and replaced with an IEEE CR followed by an IEEE LF. In the IEEE
to serial direction, the IEEE CR is unconditionally discarded. Upon receipt of
the IEEE LF a serial CR is substituted.
The interface converter can be made totally data-transparent by setting both
the serial and IEEE terminators to be CR Only or LF Only. Refer to Chapter 3
for the proper switch settings for both the IEEE and serial terminators.
33
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
4.3 IEEE Address Selection
SW3-1 through SW3-5 select the IEEE bus address of the IEEE peripheral
the interface converter will be communicating with. These switches set the
address of the IEEE device that will be controlled, not the address of the
interface converter. The address of the interface converter is automatically
adjusted so that address conflicts will not occur. The address is selected by
simple binary weighting with SW3-1 being the least significant bit and SW3-5
the most significant. If address 31 (reserved on the IEEE bus) is selected
in the controller mode, address 30 is assigned as the device it will be
communicating with. The following figure shows the IEEE address
selection of 10.
DOT
1
2
3
4
5
6
7
8
0
1
Switch
Side
View
OPEN
0 x 16 -0
1 x 8
0 x 4
1 x 2
-8
-0
-2
0 x 1 + -0
IEEE Address = 10
Figure 4-1. Switch SW3: Selecting the IEEE Address.
4.4 Talk-Back Features
Two different switch-selectable talk-back features are included to provide bi-
directional communication with the IEEE device. Whether either talk-back
feature should be enabled depends on the application.
4.4.1 TALK-BACK ON TERMINATOR
SW1-7 is used to determine whether the interface should address the attached
bus device to talk after sending the selected IEEE bus terminator(s). This
feature is commonly used to provide bidirectional communication with a
single IEEE instrument. Talk-back will only occur if there is no serial data to
output to the IEEE device. The factory default is Talk-Back On Terminator
enabled.
34
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Talk-Back on
Terminator Disabled
Talk-Back on
Terminator Enabled
Figure 4-2. Switch SW1: Enabling or Disabling
“Talk-Back on Terminator.”
When the serial input buffer becomes empty, the interface converter checks
the last characters sent to the IEEE bus device. If these were the IEEE bus
terminators and Talk-Back on Terminator is enabled, the IEEE bus device is
addressed to talk. Any data received by the interface converter from the bus
device is sent to the serial host.
When the last IEEE bus terminator is detected from the IEEE device, the
interface converter disables the device from sending additional information
by asserting Attention (ATN) on the bus.
If the IEEE device does not responded or finish transmission by the time
additional characters are received into the serial input buffer, the talk
sequence will be aborted to allow additional serial information to be sent to
the IEEE device.
The program example on the next page shows how this feature can be used to
communicate with a single IEEE instrument. The program example is written
in BASIC on an IBM PC or compatible and communicates with a Keithley
Model 196 DMM.
10
'
'
'
'
'
'
20
Example Program using interface converter with
the Talk-Back on Terminator feature enabled to
communicate with a Keithley Model 196 DMM
25
30
40
50
Open BASIC’s serial communications port
OPEN "COM1: 9600, N, 8, 2" AS 1
60
70
'
Set the Model 196 DMM to the 30VDC range
PRINT #1, "F0R3X"; ' The ; suppresses terminators
Request 10 Readings from 196”
FOR N=1 to 10
PRINT #1," " ' Output terminator
80
90
'
100
110
120
130
140
150
LINE INPUT #1, A$ ' Get reading from 196
PRINT A$ ' print it on the screen
NEXT N
END
35
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
4.4.2 TALK-BACK ON TIMEOUT
SW2-2 selects whether the interface converter should address the attached
bus device to talk when the interface converter has no more serial data to
send. This feature relies on time and not on terminators. Its use is primarily
for simulating a serial plotter from an IEEE 488 (HP-IB) plotter. The factory
default is Talk-Back On Timeout enabled.
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
Talk-Back on
Timeout Disabled
Talk-Back on
Timeout Enabled
Figure 4-3. Switch SW2: Enabling or Disabling
Talk-Back on Timeout.”
“
If Talk-Back on Timeout is enabled, the interface converter waits
approximately 100 milliseconds after it detects that its serial input buffer is
empty. If no serial character has been received by the end of this time, the
IEEE bus device is addressed to talk. The choice of talk-back modes depends
strongly on the type of device and software being used. For most plotter
applications, the Talk-Back on Timeout feature should be enabled.
When the last IEEE bus terminator is detected from the IEEE device, the
interface converter disables the device from sending additional information
by asserting Attention (ATN) on the bus. If the IEEE device does not respond
or finish transmission by the time additional characters are received into the
serial input buffer, the talk sequence will be aborted to allow additional serial
information to be sent to the IEEE device.
Most IEEE 488 plotters will not respond to the talk address sequence with
output data unless there has been a specific device dependent command
sent to tell them what to say. If they have not been told what to say, they
say nothing.
36
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
The following is an example of how this feature can be used to communicate
with an IEEE plotter. The program example is written in BASIC on an IBM
PC or compatible. It turns the PC into a dumb serial terminal. When a key
is pressed on the keyboard, the character is transmitted out of the serial
(COM1) port. Any serial data which is received from the port is printed
on the display.
10 ' Dumb Terminal Program for the interface converter
20 ' This program allows direct interaction between
30 ' the IBM PC and an IEEE plotter through the
40 ' interface converter. The interface converter must have Talk-Back
50 '
on Timeout enabled.
60 'Open the serial communications port
70 OPEN "COM1: 9600,n,8,2,cs,ds" AS 1
80 ' Display any data received from the COM1 port
90 IF LOC(1) THEN PRINT INPUT$(LOC(1),1);: GOTO 90
100 ' Transmit key presses to the COM1 port and screen
110 K$=INKEY$
120 PRINT #1, K$; : PRINT K$;
130 GOTO 90 ' Do it again
Enter the program into the computer and run it. The example below shows
®
how to test the interface converter’s operation with a Hewlett-Packard 7470A
plotter. Other IEEE plotters are similar, but you should refer to the plotter’s
programming manual for the proper command syntax. Notice the interface
converter’s front-panel LEDs as you type the plotter commands.
®
Type the following HP-GL output-identify command on the keyboard...
OI;
®
The plotter (HP 7470A) should immediately respond with.....
7470A
When you type the following HP-GL command on the keyboard, the plotter
should respond by retrieving its pen, drawing a line and returning the pen.
SP1;PA1000,1000;PD;PA1000,6000;PU;SP0;
37
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
4.5 Plotter Applications
To use the interface converter to interface an HP-IB plotter to a serial
computer port, you will need the following information about your system:
1) The serial data format that the application (plotting or graphics)
program expects the plotter to communicate with. These parameters
include baud rate, word length, stop bits, parity and serial control.
Some programs allow these parameters to be selected by the user. Other
graphics programs depend on the RS-232 version of the plotter defaults.
Usually, Hewlett-Packard plotters use 9600 baud, 7 data bits, 1 stop bit,
even parity, and X-ON/X-OFF serial control. Since these plotters are
available with serial interfaces, the operator’s manual of your IEEE
plotter should contain this information.
2) The IEEE bus address of your plotter. This address is usually set by a DIP
switch located on the rear of the plotter. The first five switches set the
address, which, for Hewlett-Packard plotters, is usually address 5. Refer
to the plotter’s operator’s manual for exact information.
Set the interface converter’s internal DIP switches to match the parameters
determined above. Other parameters which should be selected include:
1. Talk-Back on Terminator Enabled.
2. Talk-Back on Timeout Enabled.
3. Serial Terminators set to CR Only.
4. IEEE Terminators set to CR Only with EOI enabled.
38
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
RS-232
IEEE 488
Interface
Converter
Figure 4-4. A PC-Based Graphics System.
The following shows the interface converter’s internal switch settings required
®
to use a Hewlett-Packard 7580A plotter with AutoCAD from AUTODESK on
an IBM PC or compatible. Because PCs and compatibles output RS-232 levels,
the shorting DIP jumper should be set to the RS-232 position (J206).
Shorting Plug
RS-232
RS-422
Figure 4-5. Selecting RS-232 Signal Levels.
39
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
5
IEEE Addr
IEEE Term
EOI
CR Only
Enabled
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
C
Mode
Talk-Back on Timeout
Serial Term
Enabled
CR
No Echo
Even
Echo
Parity
DOT
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
9600
Baud Rate
Handshake
Word Length
X-ON/X-OFF
7 Data Bits
Enabled
Talk-Back on Terminator
Stop Bits
1 Stop Bit
Figure 4-6. Interface Converter Settings for Use with HP 7580A Plotter
on an IBM PC.
When using the interface converter with plotting programs on the Macintosh
®
computer with graphic drivers such as MacPlot , some serial data format
parameters are user-modifiable. The following is a partial MacPlot config-
uration screen which allows selection of baud rate, stop bits, and parity. With
this driver, the word length is fixed to 7 data bits with X-ON/X-OFF serial
control. These non-modifiable defaults are plotter dependent. Refer
to the plotter or driver manual for the defaults of the specific plotter.
For this example, 57600 baud with one stop bit and no parity has been
chosen for the serial data format.
40
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
File
Edit
Windows
Stop Bits:
Settings for HP 7500A
Baud Rate:
Parity:
Paper Si
1
57600
None
Apple Plotter
Graphic MP31 / 2 / 300
H.P. 7220
Houst
Houst
Houst
Houst
Houst
Houst
Houst
Houst
Houst
Calcomp 104x/7x,9x5
Calcomp 81
H.P. 7440A ColorPro
H.P. 7470A
Colorwriter 6200DS10
Colorwriter 6310
Colorwriter 6320
Epson HI-80
H.P. 7475
H.P. 7550A
H.P. 7570A DraftPro
H.P. 7580B
Facit 4551
H.P. 7585B
Graphtec FP5301
Figure 4-7. MacPlot Configuration Screen.
IEEE 488
RS-422
Interface
Converter
Figure 4-8. A Macintosh Based Graphics System.
The Macintosh computer outputs RS-422 levels. Because of this, the internal
DIP shorting jumper is set to the RS-422 position (J205).
41
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Shorting Plug
RS-232
RS-422
Figure 4-9. Setting the Internal DIP Shorting Jumper for RS-422.
The following illustrates the interface converter’s internal switch settings
for use with MacPlot, using the previously described format.
42
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 4: Controller Operation
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
5
CR
Enabled
IEEE Addr
IEEE Term
EOI
DOT
1
2
3
4
5
6 7 8
Switch
Side
View
OPEN
C
Mode
Talk-Back on Timeout
Serial Term
Enabled
CR
No Echo
No Parity
Echo
Parity
DOT
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
57600
Baud Rate
Handshake
Word Length
X-ON/X-OFF
7 Data Bits
Enabled
Talk-Back on Terminator
Stop Bits
1 Stop Bit
Figure 4-10. Interface Converter Settings for Use with HP 7580A
Plotter on a Macintosh.
After configuration, turn on the plotter and the interface converter. The
interface converter’s front-panel LEDs should all light momentarily while it
performs an internal ROM and RAM test. All LEDs should go out except for
the Power and Talk LED. The Talk LED indicates that the interface converter
has detected the plotter on the IEEE bus and has addressed it to listen.
When the serial host begins to send the interface converter data, the Receive
LED will flash. If it does not, this indicates that the interface is not receiving
data from the serial host. Verify the cables are connected properly and the
serial cable wiring. Verify the serial data format, word length, stop bits and
parity.
43
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
4.6 Printer Applications
Most of the information given for plotter applications applies to applications
for interfacing IEEE 488 printers to a serial host. Some high-end printers have
a secondary command setting which must be disabled for the interface
converter to control them. The interface converter does not use secondary
commands to control IEEE peripherals, such as printers or plotters. Refer to
the printer’s instruction manual if there is a question as to whether the
printer requires secondary commands.
44
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 5: Peripheral Operation
5. Peripheral Operation
5.1 Peripheral-Mode Operation
This mode of operation is useful in interfacing a serial device, such as a serial
printer, plotter or instrument, to an IEEE controller. Data which is sent by the
IEEE controller to the interface converter is buffered and transmitted out its
serial port. Data received from the serial device is buffered by the interface
converter until read by the IEEE controller. The interface converter can
buffer approximately 32,000 bytes of data from both the IEEE input and the
serial input.
The interface converter will refuse to accept more data from the IEEE
controller when its buffer memory is full. It does this by preventing
completion of the bus handshaking sequences. It will also request that
additional serial data not be sent by negating its Request To Send (RTS)
output or by transmitting the X-OFF ASCII character. The serial handshake
used depends on the handshake selection (see Chapter 3).
5.2 Serial and IEEE Input Buffers
Memory in the interface converter is dynamically allocated for the serial input
and IEEE input buffers. This allows for the most efficient partitioning of
memory for any given application.
At power on, or device clear, each buffer is allocated a 128-byte mini-buffer
or queue. When the serial input (or IEEE input) requires more buffer space,
additional queues are allocated. When a queue is empty, it is released from
the input buffers so that it may be re-allocated wherever it is required.
There are approximately 250 available queues for a total of 32,000 bytes of
buffer (character) space. Queues are continually allocated and released as
required by the serial and IEEE input. Of the 250 available queues, 240 are
issued without regard to controlling the receipt of additional serial or IEEE
input data.
When the serial input buffer requests one of the last 10 queues (in other
words, when there are 1280 character locations left), it signals the serial host
that it should stop sending data. This is accomplished by either unasserting
RTS or issuing “X-OFF,” depending on which serial handshake control has
been switch selected.
45
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
When more than 10 queues become available, it asserts RTS or issues “X-ON.”
The IEEE bus input signals that the IEEE input (or serial output) buffer is full
when the number of queues available drops below 10 (1280 character
locations left). When the number of available queues drops to 4 or less (512
character locations left), the IEEE interface of the interface converter stops
accepting data from the bus. This bus hold-off will only occur until additional
queues (more than 4) become available. Then the interface will resume
accepting bus data.
5.3 IEEE Data Transfers
The following methods may be used by the IEEE controller when sending
data to the interface converter:
5.3.1 BLIND BUS DATA TRANSFERS
If the IEEE controller does not mind waiting an indefinite time for data space
in the buffer to become available, the data can simply be sent to the interface
converter. This is referred to as “blind data transfer,” because the IEEE
controller is blind as to whether or not the interface converter is capable
of accepting data. In this case, the bus controller’s output data transfer will
be held off by the interface converter if it is unable to buffer the data. It will
resume accepting IEEE input data when memory becomes available. This
type of control might be appropriate in a single-user environment.
To illustrate how this would appear, let’s assume the interface converter is
connected to a serial device which will accept data at 1200 baud or 110 bytes
per second. The IEEE bus controller is capable of sending data to the
interface converter at a rate of 5000 bytes per second. The data would be
transferred on the bus at 5000 characters per second for slightly over six
seconds, filling over 31,000 locations. At that time, the IEEE input would
hold off additional data transfers until 128 characters are sent out the serial
port at rate of 110 characters per second. This 110 cps would then become
the average bus data acceptance rate of the interface converter.
If the controller is set to detect a data time-out error, then it will do so if the
interface converter holds off IEEE input data transfers for too long. The error
can be used to alert the operator to the problem, such as a printer out of
paper, so that it can be corrected. If the controller then restarts transmission
exactly where it left off, no data will be lost.
If data is requested by the controller and no serial input data is available in
the interface converter, the bus will hang until serial data is received. If no
serial data is received, it will hang forever until the controller times out.
46
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 5: Peripheral Operation
5.3.2 CONTROLLED BUS DATA TRANSFERS
If the controller must avoid waiting for the serial device, it can “serial-poll” the
interface converter. Serial polling is a method by which the controller can
inquire the internal status of the interface without disturbing any data being
transferred, slowing data transfers, or locking up the bus. You should refer to
the programming manual of your controller to determine the method of
performing serial polls.
When serial-polled, the interface converter provides eight bits of status
information to the controller. The most significant bit (DIO8) of the
interface converter’s serial poll byte is set to a logic “1” when the IEEE input
buffer is NOT EMPTY. The term NOT EMPTY is used to signify that not all
of the previous data sent to the interface has been transmitted to the serial
device. If it is NOT EMPTY, the controller may avoid sending any more data
to the interface converter. If this bit is a logic “0,” then the serial device has
accepted all previous data and the IEEE controller may send more.
Another bit (DIO4) of the Serial Poll byte is used to indicate additional
information concerning the IEEE input buffer. This bit is set to a logic “1”
when there is 1280 or less locations in the buffer for data. It is cleared, set
to a logic “0”, when there is greater than 1280 locations available. This bit is
referred to as the IEEE input buffer FULL bit.
When serial data is received, DIO5 of the Serial Poll byte is set to “1”, to
indicate to the IEEE controller that the serial input buffer is NOT EMPTY. If
this bit is set, it indicates that at least one character is available in the serial
input buffer to be read by the IEEE controller. Once all of the serial input
data is read by the IEEE controller this bit is reset.
The interface converter can generate a request for service on the bus when it
receives the last serial terminator. To enable this feature, the Peripheral SRQ
switch, located on the internal switch bank of SW1, must be enabled. When
SRQ is enabled, the interface converter will assert the IEEE bus SRQ line and
set serial poll status bits DIO7 and DIO3 when the last serial terminator is
detected. The IEEE controller must perform a serial poll on the interface to
clear the SRQ. If the Peripheral SRQ switch is in the disabled position, there
will not be any indication in the serial-poll status byte that a serial terminator
has been received.
47
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
DOT
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch
Side
View
OPEN
OPEN
SRQ on Last
Terminator Enabled
SRQ on Last
Terminator Disabled
Figure 5-1. Switch SW1: Enabling or Disabling
“SRQ on Last Terminator.”
5.4 Serial-Poll Status-Byte Register
The following shows and describes the serial-poll status information provided
by the interface converter.
DIO8
IEEE Input Buffer NOT Empty
This bit is set when the IEEE input buffer contains one
or more data bytes.
128
64
32
16
8
4
2
1
DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1
Figure 5-2. Serial Poll Status Byte.
48
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 5: Peripheral Operation
DIO7
rsv
serial-poll status information
This bit is defined by the IEEE 488 Specification and is used
to indicate to the bus controller that the interface converter is
the bus device that requested service. It is cleared when the
interface is serial polled by the controller.
DIO6
DIO5
Not Defined—Always “0”
Serial Input Buffer NOT EMPTY
This bit is set when the serial input buffer contains one or
more data bytes which have not been sent out the IEEE bus.
It is cleared, set to “0,” when the buffer is empty.
DIO4
DIO3
IEEE Input Buffer Full
When this bit is set, it indicates that the interface converter
may hold off the controller on subsequent data transfers. The
interface may continue to accept an additional 512 characters,
depending on the size of the serial input buffer.
Received Last Serial Terminator
If the Peripheral SRQ feature is enabled, the interface
converter will issue a request for service by asserting the SRQ
line and setting this bit along with the rsv bit (DIO7). It is
cleared, along with rsv, when serial polled by the controller.
If this feature is not enabled, this bit is always “0.”
DIO2
DIO1
Serial Handshake
This bit indicates the present state of the serial handshake.
If it is set to “1,” the serial device connected to the interface
converter is capable of accepting serial data. If “0,” the RTS
line is unasserted, if configured for hardware handshake, or
the “X-OFF” character has been received, if configured for
X-ON/X-OFF software handshake.
Not Used—Always “0”
49
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
5.5 Use of Serial and Bus Terminators
The interface converter can be configured to provide RS-232-to-IEEE-488 and
IEEE-488-to-RS-232 terminator substitution. This is useful when interfacing a
serial device that only issues carriage return [CR] as an output terminator to
an IEEE controller that expects a carriage return followed by a line feed
[CR-LF].
In this previous example, the serial terminator should be selected for CR
Only while the IEEE terminator is set to CR-LF. When a serial CR character is
received it is discarded and substituted with an IEEE CR followed by an IEEE
LF. In the IEEE to serial direction, the IEEE CR is unconditionally discarded.
Upon receipt of the IEEE LF a serial CR is substituted.
The interface converter can be made totally data-transparent by setting both
the serial and IEEE terminators to be CR Only or LF Only. The choice of
appropriate terminators may be determined by inspection of the serial device
and IEEE controller’s instruction manuals. See Chapter 3 of this manual for
instructions on selecting the interface converter’s serial and bus terminals.
5.6 IEEE 488 Bus Implementation
The interface converter implements many of the capabilities defined by the
IEEE 488 1978 specification. These are discussed in the following sections.
The interface converter does not support or respond to these bus uniline
and multiline commands:
Remote Enable (REN)
Go to Local (GTL)
Group Execute Trigger (GET)
Local Lockout (LLO)
Take Control (TCT)
Parallel Poll (PP)
Parallel Poll Configure (PPC)
Parallel Poll Unconfigure (PPU)
Parallel Poll Disable (PPD)
50
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 5: Peripheral Operation
5.6.1 MY TALK ADDRESS (MTA)
When the interface converter is addressed to talk, it retrieves data from
the serial input buffer and outputs it to the IEEE 488 bus. It substitutes the
selected IEEE bus terminators for the received serial terminators. The inter-
face converter will continue to output serial input buffer data as long as the
IEEE controller allows.
5.6.2 MY LISTEN ADDRESS (MLA)
When the interface converter is addressed to listen, it accepts data from the
active talker and outputs this data through the serial interface. It substitutes
the selected serial terminators for the received IEEE bus terminators.
5.6.3 DEVICE CLEAR (DCL AND SDC)
Device Clear resets the interface converter’s IEEE input and serial input
buffers. Any pending data and Service Requests (SRQ), including the
information they convey, are lost.
5.6.4 INTERFACE CLEAR (IFC)
IFC places the interface converter in the Talker/Listener Idle State. It clears
any pending requests for service (SRQ). The condition which caused the SRQ
remains unmodified.
5.6.5 SERIAL POLL ENABLE (SPE)
When Serial-Poll-Enabled, the interface converter sets itself to respond to a
serial poll with its serial-poll status byte if addressed to talk. When the serial-
poll byte is accepted by the controller, any pending SRQs are cleared. The
interface converter will continue to try to output its serial-poll response until
it is “Serial-Poll-Disabled” by the controller.
5.6.6 SERIAL POLL DISABLE (SPD)
Disables the interface converter from responding to serial polls by the
controller.
5.6.7 UNLISTEN (UNL)
UNL places the interface converter in the Listener Idle State.
5.6.8 UNTALK (UNT)
UNT places the interface converter in the Talker Idle State.
51
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
5.7 IEEE Address Selection
SW3-1 through SW3-5 select the IEEE bus address of the interface converter
when in the IEEE Peripheral mode. The address is selected by simple binary
weighting with SW3-1 being the least significant bit and SW3-5 the most
significant. The following figure shows the IEEE address of the interface
converter set to 10.
DOT
1
2
3
4
5
6
7
8
0
1
Switch
Side
View
OPEN
0 x 16 -0
1 x 8
0 x 4
1 x 2
-8
-0
-2
0 x 1 + -0
IEEE Address = 10
Figure 5-3. SW3 View for IEEE Address Selection.
Listen Only Mode
Listen Only is a special type of Peripheral operation. In the Listen Only Mode
the interface converter accepts all data transmitted on the bus and transfers it
out its serial port. The interface converter is set to Listen Only mode by
setting its address to 31 (switches SW3-1 through SW3-5 all open).
NOTE
The 232-488 Converter does not support all of these functions. Refer
back to controller mode (Section 4.1) and peripheral mode (Section 5.1)
for more information about operation of this particular device.
52
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 6: IEEE 488 Primer
6. IEEE 488 Primer
6.1 History
The IEEE 488 bus is an instrumentation-communication bus adopted by the
Institute of Electrical and Electronic Engineers in 1975 and revised in 1978.
The interface converter conforms to this most recent revision, designated
IEEE 488-1978.
Before this standard was adopted most instrumentation manufacturers
offered their own versions of computer interfaces. This placed the burden
of system hardware design on the end user. If your application required the
products of several different manufacturers, then you might need to design
several different hardware and software interfaces.
The popularity of the IEEE 488 interface (sometimes called the General
Purpose Interface Bus or GPIB) is due to the total specification of the
electrical and mechanical interface as well as the data transfer and control
protocols. The use of the IEEE 488 standard has moved the responsibility of
the user from design of the interface to design of the high-level software that
is specific to the measurement application.
6.2 General Structure
The main purpose of the GPIB is to transfer information between two or
more devices. A device can either be an instrument or a computer. Before
any information transfer can take place, it is first necessary to specify which
will do the talking (send data) and which devices will be allowed to listen
(receive data). The decision of who will talk and who will listen usually falls
on the System Controller, which is the Active Controller at power-on.
The System Controller is similar to a committee chairman. On a well-run
committee, only one person may speak at a time and the chairman is
responsible for recognizing members and allowing them to have their say.
On the bus, the device that is recognized to speak is the Active Talker. There
can only be one Talker at a time if the information transferred is to be clearly
understood by all. The act of “giving the floor” to that device is called
Addressing to Talk. If the committee chairman cannot attend the meeting, or
if other matters require his attention, he can appoint an acting chairman to
take control of the proceedings. For the GPIB, this device becomes the Active
Controller.
53
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
At a committee meeting, everyone present usually listens. This is not the case
with the GPIB. The Active Controller selects which devices will listen and
commands all other devices to ignore what is being transmitted. A device is
instructed to listen by being Addressed to Listen. This device is then referred
to as an Active Listener. Devices that are to ignore the data message are
instructed to Unlisten.
The reason some devices are instructed to Unlisten is quite simple. Suppose a
college instructor is presenting the day’s lesson. The students are told to raise
their hands if the instructor has exceeded their ability to keep up while taking
notes. If a hand is raised, the instructor stops his discussion to allow the slower
students the time to catch up. In this way, the instructor is certain that each
and every student receives all the information he is trying to present. Since
there are a lot of students in the classroom, this exchange of information can
be very slow. In fact, the rate of information transfer is no faster than the rate
at which the slowest note-taker can keep up. The instructor, though, may have
a message for one particular student. The instructor tells the rest of the class
to ignore this message (Unlisten) and tells it to that one student at a rate
which he can understand. This information transfer can then happen much
quicker, because it need not wait for the slowest student.
The GPIB transfers information in a similar way. This method of data transfer
is called handshaking. More on this later.
For data transfer on the IEEE 488, the Active Controller must:
a)Unlisten all devices to protect against eavesdroppers.
b)Designate who will talk by addressing a device to talk.
c)Designate all the devices who are to listen by addressing those devices
to listen.
d)
Indicate to all devices that the data transfer can take place.
54
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 6: IEEE 488 Primer
To Other Devices
Device 1
System Controller
Able to Talk,
Listen, and Control
Data Bus
Device 2
DMM
Able to Talk
and Listen
Data Byte
Transfer
Control
Device 3
Printer
Only Able to Listen
General
Interface
Management
Device 4
Frequency Counter
Only Able to Talk
DIO1-8
DAV
NRFD
NDAC
IFC
ATN
SRQ
REN
EOI
Figure 6-1. IEEE 488 Bus Structure.
6.3 Send It to My Address
In the previous discussion, the terms “Addressed to Talk” and “Addressed to
Listen” were used. These terms require some clarification.
The IEEE 488 standard permits up to 15 devices to be configured within one
system. Each of these devices must have a unique address to avoid confusion.
In a similar fashion, every building in town has a unique address to prevent
one home from receiving another home’s mail. Exactly how each device’s
address is set is specific to the device’s manufacturer. Some are set by DIP
switches in hardware, others by software. Consult the manufacturer’s
instructions to determine how to set the address.
Addresses are sent with universal (multiline) commands from the Active
Controller. These commands include My Listen Address (MLA), My Talk
Address (MTA), Talk Address Group (TAG), and Listen Address Group
(LAG).
55
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
6.4 Bus Management Lines
Five hardware lines on the GPIB are used for bus management. Signals on
these lines are often referred to as uniline (single line) commands. The
signals are “active low”: A low voltage represents a logical “1” (asserted),
and a high voltage represents a logical “0” (unasserted).
6.4.1 ATTENTION (ATN)
ATN is one of the most important lines for bus management. If Attention is
asserted, then the information contained on the data lines is to be interpreted
as a multiline command. If it is not, then that information is to be interpreted
as data for the Active Listeners. The Active Controller is the only bus device
that has control of this line.
6.4.2 INTERFACE CLEAR (IFC)
The IFC line is used only by the System Controller. It is used to place all bus
devices in a known state. Although device configurations vary, the IFC
command usually places the devices in the Talk and Listen Idle states
(neither Active Talker nor Active Listener).
6.4.3 REMOTE ENABLE (REN)
When the System Controller sends the REN command, bus devices will
respond to remote operation. Generally, the REN command should be issued
before any bus programming is attempted. Only the System Controller has
control of the Remote Enable line.
6.4.4 END
OR
IDENTIFY (EOI)
The EOI line is used to signal the last byte of a multibyte data transfer. The
device that is sending the data asserts EOI during the transfer of the last data
byte. The EOI signal is not always necessary, as the end of the data may be
indicated by some special character such as carriage return.
The Active Controller also uses EOI to perform a Parallel Poll by
simultaneously asserting EOI and ATN.
6.4.5 SERVICE REQUEST (SRQ)
When a device desires the immediate attention of the Active Controller it
asserts SRQ. It is then the Controller’s responsibility to determine which
device requested service. This is accomplished with a Serial Poll or a Parallel
Poll.
56
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 6: IEEE 488 Primer
6.5 Handshake Lines
The GPIB uses three handshake lines in an “I’m ready—Here’s the data—I’ve
got it” sequence. This handshake protocol assures reliable data transfer, at the
rate determined by the slowest Listener. One line is controlled by the Talker,
while the other two are shared by all Active Listeners. The handshake lines,
like the other IEEE 488 lines, are active low.
6.5.1 DATA VALID (DAV)
The DAV line is controlled by the Talker. The Talker verifies that NDAC is
asserted (active low) which indicates that all Listeners have accepted the
previous data byte transferred. The Talker then outputs data on the bus and
waits until NRFD is unasserted (high) which indicates that all Addressed
Listeners are ready to accept the information. When NRFD and NDAC are
in the proper state, the Talker asserts DAV (active low) to indicate that the
data on the bus is valid.
6.5.2 NOT READY FOR DATA (NRFD)
This line is used by the Listeners to inform the Talker when they are ready to
accept new data. The Talker must wait for each Listener to unassert this line
(high), which they will do at their own rate when they are ready for more
data. This assures that all devices that are to accept the information are ready
to receive it.
6.5.3 NOT DATA ACCEPTED (NDAC)
The NDAC line is also controlled by the Listeners. This line indicates to the
Talker that each device addressed to listen has accepted the information.
Each device releases NDAC (high) at its own rate, but the NDAC will not
go high until the slowest Listener has accepted the data byte.
57
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
1st Data Byte
2nd Data Byte
DIO-8
(composite)
DAV
Source
Valid
Not
Valid
None
Not
Valid
Valid
All
Ready
None
Ready
All
NFRD
Acceptor
Ready
Ready
None
Accept
All
None
All
Accept
NDAC
Acceptor
Accept Accept
Figure 6-2. IEEE Bus Handshaking.
6.6 Data Lines
The GPIB provides eight data lines for a bit-parallel/byte-serial data transfer.
These eight data lines use the convention of DIO1 through DIO8 instead of
the binary designation of D0 to D7. The data lines are bidirectional and are
active low.
6.7 Multiline Commands
Multiline (bus) commands are sent by the Active Controller over the data bus
with ATN asserted. These commands include addressing commands for talk,
listen, Untalk, and Unlisten.
6.7.1 GO
TO
LOCAL (GTL)
This command allows the selected devices to be manually controlled. ($01)
6.7.2 LISTEN ADDRESS GROUP (LAG)
There are 31 (0 to 30) listen addresses associated with this group. The 3 most
significant bits of the data bus are set to 001, while the 5 least significant bits
are the address of the device being told to listen.
58
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 6: IEEE 488 Primer
6.7.3 UNLISTEN (UNL)
This command tells all bus devices to Unlisten. The same as Unaddressed to
Listen. ($3F)
6.7.4 TALK ADDRESS GROUP (TAG)
There are 31 (0 to 30) talk addresses associated with this group. The 3 most
significant bits of the data bus are set to 010 while the 5 least significant bits
are the address of the device being told to talk.
6.7.5 UNTALK (UNT)
This command tells bus devices to Untalk. The same as Unaddressed to Talk.
($5F)
6.7.6 LOCAL LOCKOUT (LLO)
Issuing the LLO command prevents manual control of the instrument’s
functions. ($11)
6.7.7 DEVICE CLEAR (DCL)
This command causes all bus devices to be initialized to a predefined or
power-up state. ($14)
6.7.8 SELECTED DEVICE CLEAR (SDC)
This causes a single device to be initialized to a pre-defined or power-up state.
($04)
6.7.9 SERIAL POLL DISABLE (SPD)
The SPD command disables all devices from sending their Serial Poll status
byte. ($l9)
6.7.10 SERIAL POLL ENABLE (SPE)
A device which is Addressed to Talk will output its Serial Poll status byte after
SPE is sent and ATN is unasserted. ($18)
6.7.11 GROUP EXECUTE TRIGGER (GET)
This command usually signals a group of devices to begin executing a
triggered action. This allows actions of different devices to begin
simultaneously. ($08)
59
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
6.7.12 TAKE CONTROL (TCT)
This command passes bus control responsibilities from the current Controller
to another device which has the ability to control. ($09 )
6.7.13 SECONDARY COMMAND GROUP (SCG)
These are any one of the 32 possible commands (0 to 31) in this group. They
must immediately follow a talk or listen address. ($60 to $7F)
6.7.14 PARALLEL POLL CONFIGURE (PPC)
For devices capable of performing a Parallel Poll, this command determines
which data bit they are to assert in response to a Parallel Poll ($05)
6.7.15 PARALLEL POLL UNCONFIGURE (PPU)
This disables all devices from responding to a Parallel Poll. ($15)
6.8 More on Service Requests
Most of the commands covered, both uniline and multiline, are the
responsibility of the Active Controller to send and the bus devices to
recognize. Most of these happen routinely by the interface and are totally
transparent to the system programmer. Other commands are used directly by
the user to provide optimum system control. Of the uniline commands, SRQ
is very important to the test system, and the software designer has easy access
to this line by most devices. Service Request is the method by which a bus
device can signal to the Controller that an event has occurred. It is similar to
an interrupt in a microprocessor-based system.
Most intelligent bus peripherals have the ability to assert SRQ. A DMM might
assert it when its measurement is complete, if its input is overloaded or for
any of an assortment of reasons. A power supply might SRQ if its output has
current limited. This is a powerful bus feature that removes the burden from
the System Controller to periodically inquire, “Are you done yet?” Instead, the
Controller says, “Do what I told you to do and let me know when you’re done”
or “Tell me when something is wrong.”
Since SRQ is a single line command, there is no way for the Controller to
determine which device requested the service without additional information.
This information is provided by the multiline commands for Serial Poll and
Parallel Poll.
60
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 6: IEEE 488 Primer
6.8.1 SERIAL POLL
Suppose the Controller receives a service request. For this example, let’s
assume there are several devices which could assert SRQ. The Controller
issues an SPE (Serial Poll enable) command to each device sequentially. If
any device responds with DIO7 asserted, it indicates to the Controller that it
was the device that asserted, SRQ. Often the other bits will indicate why the
device wanted service. This Serial Polling sequence, and any resulting action,
is under control of the software designer.
6.8.2 PARALLEL POLL
The Parallel Poll is another way the Controller can determine which device
requested service. It provides the who but not necessarily the why. When bus
devices are configured for Parallel Poll, they are assigned one bit on the data
bus for their response. By using the Status bit, the logic level of the response
can be programmed to allow logical OR/AND conditions on one data line by
more than one device. When SRQ is asserted, the Controller (under user’s
software) conducts a Parallel Poll. The Controller must then analyze the eight
bits of data received to determine the source of the request. Once the source
is determined, a Serial Poll might be used to determine the why.
Of the two polling types, the Serial Poll is the most popular due to its ability
to determine the who and why. In addition, most devices support Serial Poll
only.
61
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
7. Theory of Operation
and Board Layout
7.1 Theory of Operation
The heart of the interface converter is a 6809 microprocessor (U101)
supported by 8K bytes of firmware EPROM [U102 (2764)] and 32K bytes of
static RAM [U103 (58256)]. A Versatile Interface Adapter [U104 (65B22)]
is used to generate real-time interrupts for the firmware operating system.
The front-panel annunciators are also driven by U104 through an inverter
[U113 (74LS04)]. The IEEE 488 bus interface is accomplished by a
TMS9914A [U106] controller with drivers U107 and U108. The serial
interface is provided by the UART [6551 (U105)]. If RS-232 levels are chosen,
they are provided by the RS-232 transceiver (U209). If RS-422 levels are
selected, the differential driver [26LS30 (U207)] and receiver [26LS33
(U208)] are used.
The internal DIP switches [SW1, SW2, and SW3] are read via 74HCT244
tri-state buffers [U201, U202 and U203]. Power is supplied by an external
unregulated 9-volt wallmount supply. Regulation to the required +5 volts is
provided by U206 [7805].
Decoding of the microprocessor address space is accomplished with a
Programmable Logic Array [U110 (16L8)]. The Memory space allocation is:
Address
$0000-$7FFF
$A000-$A007
$A800-$A807
$B000-$B00F
$B800
Device
U103
U106
U105
U104
U201
U202
U203
U102
Part Number
58258
Function
Static RAM
IEEE Controller
UART
9914A
6551
65B22
74HCT244
74HCT244
74HCT244
2764
VIA
SW1 (S201)
SW2 (S202)
SW3 (S203)
Programmed EPROM
$B801
$B802
$E000-$FFFF
62
Download from Www.Somanuals.com. All Manuals Search And Download.
CHAPTER 7: Theory of Operation and Board Layout
7.2 Board Layout
J104
U110
U101
R102
C124
U107
U108
Figure 7-1. Component Layout of the
Interface Converter’s Motherboard.
63
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
U201
P204
R205
R201
R202
R203
C201
C202
C203
U205
U206
C205
C209
C207
R207
1
14
C208
Figure 7-2. Component Layout of the
Interface Converter’s Serial I/O board.
64
Download from Www.Somanuals.com. All Manuals Search And Download.
APPENDIX A: Sample Dumb-Terminal Program
Appendix A. Sample Dumb-Terminal
Program
10
REM ***
DUMB-TERMINAL PROGRAM FOR THE interface
converter
20
30
40
REM ***
REM ***
REM ***
Running under IBM BASIC
This Program allows direct interaction between the
IBM PC and an IEEE bus device through the interface
converter.
50
REM ***
The interface converter must be configured as the
IEEE bus
controller and have Talk-Back on Terminator enabled.
60
70
80
90
100
REM ***
REM ***
REM ***
REM ***
CLS
110 ' Open the serial communications port and set the serial parameters
120 OPEN "COM1: 9600,n,8,2,cs,ds" AS 1
130 ' Display any characters received from the COM1 port
140
IF LOC(1) THEN PRINT INPUT$ (LOC(1) ,1);
150 ' Transmit any key presses from keyboard to the COM1 port and to
the screen
160 K$=INKEY$
170 PRINT #1,K$; : PRINT K$;
180 GOTO 140 ' Do it again
65
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Appendix B. Character Codes and IEEE
Multiline Messages
$00
0 $10
16 $20
32 $30
48 $40
64 $50
80 $60
96 $70
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SP
0
1
2
3
4
5
6
7
8
9
:
@
A
B
C
D
E
F
P
Q
R
S
T
U
V
W
X
Y
Z
[
`
a
b
c
d
e
f
p
16
00
17 $21
16
33 $31
00
49 $41
SCG
97 $71
SCG
81 $61
$01
1 $11
65 $51
!
q
17
66 $52
17
34 $32
SCG
82 $62
LLO
2 $12
01
18 $22
01
50 $42
GTL
$02
SCG
98 $72
"
r
18
67 $53
02
51 $43
02
19 $23
18
35 $33
SCG
83 $63
SCG
99 $73
$03
$04
3 $13
4 $14
#
$
%
&
'
s
19
68 $54
19
36 $34
SCG
84 $64
SCG
100 $74
03
20 $24
03
52 $44
t
20
37 $35
20
69 $55
DCL
5 $15
SCG
101 $75
SDC
$05
04
21 $25
04
53 $45
SCG
85 $65
u
21
70 $56
05
22 $26
21
38 $36
SCG
86 $66
SCG
102 $76
PPC
$06
PPU
6 $16
05
54 $46
v
22
22
39 $37
06
23 $27
SCG
87 $67
SCG
103 $77
06
55 $47
$07
$08
7 $17
8 $18
71 $57
G
H
I
g
h
i
w
SCG
88 $68
23
40 $38
07
24 $28
07
56 $48
23
72 $58
SCG
104 $78
(
x
08
25 $29
GET
$09
SPE
9 $19
SCG
89 $69
SCG
105 $79
24
41 $39
08
57 $49
24
73 $59
HT
)
y
SPD
10 $1A
09
26 $2A
SCG
106 $7A
TCT
$0A
25
42 $3A
09
58 $4A
25
74 $5A
SCG
90 $6A
LF
SUB
ESC
FS
*
+
,
J
j
z
10
59 $4B
SCG
91 $6B
10
27 $2B
26
43 $3B
26
75 $5B
SCG
107 $7B
$0B
$0C
$0D
$0E
$0F
11 $1B
12 $1C
13 $1D
14 $1E
15 $1F
VT
;
K
L
M
N
O
k
l
{
27
76 $5C
11
60 $4C
SCG
92 $6C
SCG
108 $7C
11
28 $2C
27
44 $3C
FF
<
=
>
?
\
|
}
12
29 $2D
28
45 $3D
SCG
93 $6D
12
61 $4D
28
77 $5D
SCG
109 $7D
CR
GS
-
]
m
n
o
13
62 $4E
29
78 $5E
SCG
110 $7E
13
30 $2E
29
46 $3E
SCG
94 $6E
SO
RS
.
^
~
14
63 $4F
30
47 $3F
30
79 $5F
SCG
95 $6F
14
31 $2F
SCG
111 $7F
SI
US
/
_
DEL
15
UNT
15
SCG
SCG
UNL
ACG = Addressed Command Group
UCG = Universal Command Group
LAG = Listen Address Group
TAG = Talk Address Group
SCG = Secondary Command Group
66
Download from Www.Somanuals.com. All Manuals Search And Download.
APPENDIX B: Character Codes and IEEE Multiline Messages
How To Read the Chart
Hexadecimal
Equivalent
Decimal
Equivalent
ASCII Character
Address or Command
67
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Index
Abbreviations
DIO4...............................................49
IEEE 488 .................................13
DIO5...............................................49
DIO6...............................................49
DIO7...............................................49
DIO8...............................................48
Echo................................................19
End Or Identify .............................56
EOI22, 56
Active Controller ...........................53
Address Selection
IEEE ........................................34
Applications
Plotter .....................................38
Printer.....................................44
ATN ................................................56
Attention ........................................56
Baud Rate.......................................16
Blind Bus Data Transfers ..............46
Board Layout ...........................63, 64
Bus Management Lines
Attention.................................56
End Or Identify ......................56
Interface Clear........................56
Remote Enable.......................56
Service Request.......................57
CE Compliant
Operating Conditions .....................2
Character Codes ............................66
Clear To Send................................27
Configuration ................................14
Connectors...............................26, 27
Controlled Bus Data Transfers .....47
Controller Features .......................24
Controller Mode Operation .........32
Controller Operation....................32
Data Lines ......................................58
Data Transfers
Blind Bus.................................46
Controlled Bus .......................47
Data Valid.......................................57
DAV ................................................57
DCL ..........................................51, 59
Device Clear.............................51, 59
DIO1...............................................49
DIO2...............................................49
DIO3...............................................49
Factory-Default Settings ..........14, 15
Feature Selections .........................24
Controller ...............................24
Peripheral...............................25
Features
Talk Back ...........................34-36
General Purpose
Interface Bus..................................53
GET ................................................59
Go To Local ...................................58
GPIB ...............................................53
Ground...........................................28
Group Execute Trigger.................59
GTL ................................................58
Handshake Lines...........................57
Data Valid ...............................57
Not Data Accepted.................57
Not Ready For Data................57
IEEE 488 Abbreviations.................13
IEEE 488 Bus
Implementation.............................50
IEEE 488 Primer............................53
IEEE Address Selection.....23, 34, 52
IEEE Bus Terminator....................22
IEEE Controller
Mode ............................16, 22, 23, 32
IEEE Data Transfers ......................46
IEEE Multiline Messages...............66
IEEE Peripheral.............................16
IFC ...........................................51, 56
Input Buffers..................................45
Inspecting the Unit .......................14
68
Download from Www.Somanuals.com. All Manuals Search And Download.
INDEX
Interface Clear.........................51, 56
Interface Converter
Package Contents ..........................14
Parallel Poll....................................61
Parallel Poll Configure..................60
Parallel Poll Unconfigure .............60
Peripheral Features .......................25
Peripheral Mode......................22, 23
Peripheral Operation....................45
Plotter Applications.......................38
Polling Types
Parallel ....................................61
Serial .......................................61
POWER Indicator..........................31
PPC60
PPU.................................................60
Printer Applications ......................44
Receive Data...................................27
Receive Data Plus...........................28
Remote Enable ..............................56
REN ................................................56
Request To Send............................28
RS-232 Signals.....................26-28, 39
RS-422 Signals...........................26-28
RTS/CTS............................20, 27, 28
Sample Program ............................65
SCG.................................................60
SDC...........................................51, 59
Secondary Command Group........60
Selectable Functions......................14
Selected Device Clear....................59
Selecting an IEEE Address............52
Selecting Terminator
Connectors.....................................26
Introduction...................................12
LAG ................................................58
LEDs ...................................31, 37, 43
Listen Address Group....................58
Listen Only...............................23, 52
LLO ................................................59
Local Lockout................................59
MLA................................................51
Mode
Selection .................................22
Modifying Factory Defaults...........16
MTA................................................51
Multiline Commands.........50, 56, 58
Device Clear............................59
Go To Local............................58
Group Execute Trigger..........59
Listen Address Group ............58
Local Lockout.........................59
Parallel Poll Configure ..........60
Parallel Poll Unconfigure......60
Secondary Command
Group......................................60
Selected Device Clear ............59
Serial Poll Disable ..................59
Serial Poll Enable...................59
Take Control ..........................60
Talk Address Group...............59
Unlisten ..................................59
Untalk .....................................59
My Listen Address..........................51
My Talk Address ............................51
NDAC .............................................57
Not Data Accepted ........................57
Not Ready For Data .......................57
NRFD..............................................57
Operation
Substitution....................................21
Selecting the IEEE Address...........23
Selecting the Mode........................22
Self-Check ......................................31
Send It to My Address ...................55
Serial and IEEE Input Buffers ......45
Serial and IEEE Terminator
Substitution....................................33
Serial Baud Rate ............................16
Serial Echo.....................................19
Serial Handshake...........................19
Serial Interface ..............................25
Controller ...............................32
General .............................30, 31
Peripheral...............................45
Theory.....................................62
69
Download from Www.Somanuals.com. All Manuals Search And Download.
RS-232↔IEEE 488 INTERFACE CONVERTER
Serial Parity ....................................18
Serial Poll .......................................61
Serial Poll Disable....................51, 59
Serial Poll Enable ....................51, 59
Serial Port Settings ........................16
Serial Signal Descriptions .............26
Serial Terminator ..........................21
Serial-Poll Status
UNT..........................................51, 59
Untalk.......................................51, 59
Wiring Diagrams............................29
IBM AT with DB9
Connector to Interface
Converter................................30
IBM PC with DB25
Connectors to Interface
Information..............................48, 49
Serial-Poll Status-Byte
Converter................................29
Macintosh to Interface
Register...........................................48
Service Requests ......................57, 60
Shorting Plug.....................25, 26, 42
Signal Level Selection ...................26
SPD51, 59
SPE ...........................................51, 59
Specifications
Converter................................29
X-ON/X-OFF.....................20, 27, 28
General ...................................11
IEEE-488 Interface .................10
Serial Interface .......................10
SRQ.................................................57
SW1.............17, 18, 20, 24, 25, 35, 48
SW2................................19, 21-24, 36
SW3.....................................22, 23, 34
System Controller..........................53
TAG ................................................59
Take Control..................................60
Talk Address Group ......................59
Talk-Back Features ........................34
Talk-Back on Terminator..............35
Talk-Back on Timeout...................36
TCT ................................................60
Terminator Substitution ...............21
Serial and IEEE ......................33
Terminators ...................................50
Test Voltage ...................................28
Theory of Operation .....................62
Transmit Data ................................27
Transmit Data Plus ........................28
Uniline Commands .......................50
UNL..........................................51, 59
Unlisten..............................51, 54, 59
Unpacking......................................14
70
Download from Www.Somanuals.com. All Manuals Search And Download.
© Copyright 1998. Black Box Corporation. All rights reserved.
1000 Pasrk Drive • Lawrence, PA 15055-1018 • 724-746-5500 • Fax 724-746-0746
Download from Www.Somanuals.com. All Manuals Search And Download.
|